It is well known that bedrest is associated with loss of muscle in younger persons and with persons put on bedrest for experimental purposes. Dr. William Evans and Dr. Nick Hays have demonstrated that there is almost double the loss of muscle tissue in older persons compared with younger persons on 10 days of bedrest. In these protocols, he obtains muscle tissue from biopsy and has shown an that muscle breakdown is greater older compared to younger persons. He uses dual energy x-ray absorptiometry to quantify muscle in these protocols. Use of computerized tomography in these experiments will allow extension of this work to examine the specific effect of bedrest on atrophy of particular muscle groups, on change in intermuscular adipose, and on change in muscle attenuation, an indicator of the infiltration of adipose into muscle below the level of resolution needed to define aggregate adipose tissue. These effects can be correlated to the physiologic measurements already planned in Dr. Evan's current bedrest experiment, including measures of hepatic glucose uptake and hepatic insulin resistance as well as peripheral insulin resistance and protein synthesis. In addition, because each participant is giving a 60 day rehabilitation period, we can assess whether the structural changes secondary to bedrest are completely reversed.